The effect of external N and K concentrations on the leaf content of monovalent cations and their forms in capsicum plants

Capsicum plants (Capsicum annuum L. cv. Lamuyo) were grown in controlled gr eenhouse conditions. The crop underwent fertirrigation with different level s of N and K, with a complement of other essential nutrients. The plants we re sampled periodically to determine leaf levels of total and soluble K and Na. Both nutrients can be used for the diagnosis of physiologically active endogenous levels. Endogenous levels may or may not depend on the exogenou s level. Soluble Na showed low levels in the N group with the lowest rhizos pheric N levels, with a minimum when K concentrations in the growth medium were also low (T-2), while T-4 showed a higher leaf concentration although the presence of N and K in the rhizosphere was not significant. Total Na le vels were more closely linked to doses applied, with the minimum leaf level occurring when the external concentration was lowest and the maximum when it was highest, although with the lowest K concentration. Soluble K was ver y closely related to external K levels, rather than to the amounts of N app lied. The soluble K+soluble N and soluble K/soluble Na ratios confirmed the total dominance of univalent cations in treatments with high levels of K, regardless of how much N was applied. Soluble forms of the two cations show ed the differences between treatments more clearly than the total forms, as did the ratios. This would suggest that the sum and its ratio provide a di scriminatory system which enables the characteristics of the effect of fert ilizer to be accurately determined, as individual study of both cations wou ld not be possible. In the present study Na levels were not particularly hi gh, in comparison with the K levels obtained.